Manufacture of propeller blades



June 10, 1947. D. J. MccoMB MANUFACTURE 0F' PROPELLERVBLADES Filed Jan. 29, 1944 5 SheetsfSheet 1 June 10, 1947. n.1. MCCOMB 2,421,956

MANUFACTURE 0F PROPELLER BLADES Hum i aff INVENTOR ATTORN June 10, 1947. D, `),MCCQMB MANUFACTURE 0F PROPELLER BLADES `Filed Jan. 29, 1944 3 Sheets-Sheet 3 Patented June 10, 1947 MANUFACTURE 0F PROPELLER BLADES i David J. McComb, Emsworth, Pa., assignor `to Curtiss-Wright Corporation, a corporation of Delaware aiipueauon January 29, 1944, serial No. 520,361

a claims. (c1. ca -156.8) l

rough-turned shank of the propeller blade, there- Vby producing a new shank surface in desired position relative to said reference line or surface, this machining being done after said iirst-named blade surfaces or said center of gravity, or both have been located in predetermined position relative to said reference line.

A more specific form of my invention involves A the use of a tubular sleeve adapted to receive and retain th'e rough-turned propeller shank therein. Means are provided for adjusting the position of said propeller blade relative to the extended longitudinal axis of said sleeve which acts as the having a longitudinally-extending central groove la. A plurality of suitably spaced index lines Ib extend transversely of the base l, these lines designating different stations as known inthe propeller blade manufacturing art. i

Secured to the base l by suitable clamps 2a is the head 2 comprising the lower section 2b and a complementary upper section 2c hinged thereto. The upper section 2c may be heldin engagement with the lower section 2b by the clamps 2d. In suoli' engaged position, said upper section 2c and Vsaid lower section 2b mutually define a central cylindrical passage 2e extending longitudinally of the base l. Y 'i The base I further carries a measuring device 3 slidably supported upon the base l bythe blocks 3a and the'plate 3b, which comprises a tongue, not shown, disposed within the aforesaid groove la together with a transverse surface 3c which inwith' respect to the aforesaid index lines Ib.` Integral with said sliding blocks 3a and `said plate 3b is the transverse memberl 3d comprising a transverse groove 3e in which the triangular templates 3f, 3f may slide, the respective inner surfaces 3g o! said templates 3f being perpendicular Figs. 4 and 5 are schematic views showing feaf tures of the invention;

Fig. 6 is a perspective view showing a, blade balancing apparatus as used in my invention;

Fig. '7 is a side elevational View, partially in section, illustrating another use of the balance stand in accordance with the invention;

Figs. 8 and 9 are schematic views illustrating features of the invention;

Fig. 10 is a reduced side view showing the application of my invention to a modified form of propeller blade; and i Figs. 11 and 12 are diagrammatic views illustrating the use of a lathe in accordance with my to said transverse groove 3e. The transverse member 3d carries a scale 3h, reading outwardly in both directions from the center, said scale 3h. being adapted to measure the distance of the respective inner surfaces 3g of the templates 3f from its mid-point or zero-point Il which is included in the vertical plane VP determined by th'e extended longitudinal axis of the passage 2e.

Referring to Fig. 6, I have shown a blade-balancing apparatus consisting of suitable blocks 4 supporting the balance stands la, respectively, which, in turn, support the respective ways 4b, the respective upper surfaces 4d of which are at the same level and spaced in parallel relation.

A tubular balance hub 5 comprises the centrally located, transverse, diametrcal pin 5a, the extremities of which are adapted to rest, in rolling contact, upon the upper surfaces 4d of the ways The balance hub 5 further comprises l 3 The lower end oi' the rod 8 carries the threaded weights 8a which are adjustable vertically with respect thereto.

The blade balancing apparatus is carefully constructed in order that its center of gravity will be on the longitudinal axis of the' balance hub 5.

Referring to Figs. 11 and 12, I have shown a part of the stationary structure 'I of a lathe in which is journalled a cradle l which may be rotated by any suitable source of power, not shown, said cradle 8 comprising the tubular head 8a integral with the spaced longitudinally extending t plates 8b. Y

III, Figs. l, 2 and 3, of novel construction and function "which comprises a tubular shank II corresponding diametrically with and adapted to be snugly received Vin the cylindrical passage 2e of the reading head 2, said tubular shank II having the circumferential slots IIa, which are machined to accurate circula;- configuration. disposedA near the respective ends thereof.' Integrally formed andin axial alignment with said tubular shank II is a tubular head I2.

The tubular head." carries two pairs of set screws Ila, IIb, and two other pairs oi' set screws llc, I3d,-the screws of each pair being transversely alined in facing relation. 'I'he two pairs of set screws Ila, I3b /are offset with respect to each other by` an angle of ninety degrees and they are spaced equal distances from the inner end of the tubular head I2. Similarly, the two pairs of set-screws I3c, i3d are offset with respect to each other by an angie of ninety degrees and they are spaced equal distances from the outer endoi'said tubular head I2. The Just-described apparatus is utilized, as disclosed below,

for the practice of my novel propeller blade balancing method. Y

Referring now to Fig. l, the first step is to place the tubular shank Il of the sleeve III upon the open'lower section 2b of the head 2. The upper section 2c is then swung into facing position with respect to the lower section 2b and the clamps 2d are tightened to cause said upper surface 2c to engage said lower surface 2b, thereby ilrmly securing said tubular shank II in seated position within the head 2. a

In such seated position, the extended longitudinal axis S of the sleeve I0 is parallel to the base I and the vertical plane VP determined by said extended axis S intersects the scale 3h. at its zero-point 0 for any position oi' the measuring device 3 longitudinally of the .base I.

Accordingly, for any such position of the measuring device 3, the distance of the respective inner surfaces 3g of the templates 3f from the extended axis S of the sleeve I0 may be read upon the scale 3h.

iis shown and preferably, the sleeve I0 is first seated within the head 2 in such position that the set screws I3a, I3c lie in a vertical plane and the set screws IIb, I Id lie in a horizontal plane which position will be hereinafter referred to as position X. For a purpose described later, the sleeve I0 may be rotated 90 degrees with respect to the head 2 to a position Y, in which the set screws Ila, I3c lie in a horizontal plane and the set screws I3b, i3d lie in a vertical plane.

In the second step of my blade-balancing method, the sleeve III being in position X, the sets of set screws I3a, I3b, I3c, I3d are retracted and the shank 9a of a propeller blade 9 is placed within the tubular head I2 of the sleeve I0, in such position that the edge 3g of one of the templates 3f engages the approximately fiat thrust plate A of the blade 9 substantially throughout its length at a suitable station, preferably the 42" station. Thus, the thrust plate A is perpendicular to the base I at the 42" station.. 'I'he set screws I3c, I3d are then tightened into engagement with the blade shank 9a, thereby preventing rotation of the blade 9 with respect to the sleeve II) with the result that the thrust plate A will be perpendicular to the base I at the 42" station whenever the sleeve I0 is in the described position X with' respect to the head 2. Those skilled in the art will understand that the thrust plate A will form an angle with the perpendicular at the other stations, this angle increasing in a progressive manner with the distance from the 42" station.

The third step in my blade-balancing method is to center a circular blade section 9b, adjacent the shank 9a, with respect to the extended axis of the sleeve I0. As shown by Fig. 4, at this stage, the centerC of said circular section 9b is usually offset both horizontally and vertically from the extended sleeve axis S.

This centering step is done as follows: The blade sleeve unit being in position X, the measuring device 3 is moved to a position near the shank of the blade and the templates 3f are placed in contact with the circular section 9b engaging it at the surfaces a, a, respectively, Fig. 4, the line al joining said surfaces a, a, being the horizontal diameter of the circular section 9b and the center of the line al being the center C of the circular section 9b. For each of the surfaces a, a there is a corresponding'reading on the scale 3h, the midpoint 0 of which, as previously described, is included in the vertical plane VP determined by the extended sleeve axis S. 'I'hese readings, therefore, show the respective distances of the surfaces a, a from said vertical plane VP.

If said surfaces a, a are equidistant from said vertical plane VP, the horizontal diameter al of the circular section 9c is centrally intersected by said vertical plane VP. The center C 0f the circular section 9b accordingly lies on the vertical plane VP determined by the extended axis S of the sleeve I0.

Usually, however, these surfaces a, a are not equidistant from said vertical plane VP. Therefore, by tightening one of the set screws I3'd, Figs. land 3, and loosening the other set screw i3d, the blade, including the circular section 9b, is moved horizontally with respect to the vertical plane VP determined by the extended sleeve axis S, the surfaces a, a moving horizontally with respect to the scale 3h, for example, in the direction of the arrow, Fig. 4. This operation, involving use of the templates 3f and adjustment of the set screws I3d, i3d is repeated several times, if necessary. Finally, the respective distances of the surfaces a, a from the vertical plane VP determined by the extended sleeve axis S are equalized and the center C of the circular section 9b lies upon said vertical plane VP. Thus, the circular section 9b is centralized with respect to the vertical plane VP determined by the extended sleeve axis S. It will be understood that, at this stage, the center C of the circular section 9b is To center the circular section 9b with respect to the extended sleeve axis S, it is now necessary to move said circular section 9b vertically relative to said extended sleeve axis S until the center C of the circular section 9b coincides with the extended sleeve axis S. To this end, the bladesleeve unit is rotated 90 degrees with respect to the head 2 to position Y, the circular section 9b moving eccentrically relative to the extended sleeve axis S and the center C of the circular section 9b moving from a vertically offset position to a horizontally offset position with respect' to said extended sleeve axis S, as shown in Fig. 5.

The templates 3f are againv placed in contact with the circular section 9b engaging it at the surfaces b, b respectively, Fig. 5, the line bl joining said surfaces b, b being the new horizontal diameter of the circular section 9b and the midpoint of the line bl being the center C of the circular section 9b. Since the extended sleeve axis S is now horizontally offset 'from the center C of the circularsection 9b, it is also included on the horizontal diameter bi. For each surface b, b there is a corresponding reading on the scale 3h, the midpoint of which corresponds to the intersection of the extended sleeve axis S and the horizontal diameter bl of the circular section 9b. These readings, therefore, show the respective distances of the surfaces b, b from the extended sleeve axis S.

If these distances are equal, the surfaces b, b are equidistant from the sleeve axis S which will then be at the center C of the horizontal diameter bl. The center C of the circular section 9b accordingly coincides `with the extended axis S of the sleeve Ill.

Usually, however, these distances are unequal. Therefore, by tightening one of the set screws |3c, Figs. 1 and 2, and'loosening the other set screw IBC, the blade, including the circular section 9b. is moved horizontally with respect to the extended sleeve axis S, the surfaces b, b moving' horizontally with respect to the scale 3h, for example, in the direction shown by the arrow, Fig. 5. This operation, involving use of the templates 3f and adjustment of the set screws |3c, l3c is re-` peated several times, if necessary. Finally. the respective distances of the surfaces b, b from the extended sleeve axis S are equalized and the center C of the circular section 9b is coincident with the extended sleeve axis S. This centralizes the circular section 9b with respect to the extended sleeve axis S.

The set screws I3a, I3a and |317, 13b are then tightened into engagement with the blade shank. this tightening having no effect on theset screws I 3c, i3c and i3d, i3d and the centered position of the circular section 9b maintained thereby.

Referring to Fig. 3, the fourth step is to place the surface of the thrust plate A at a suitable station, for example, the 42" station. a known specified distance c fromthe extended axis S of the sleeve Il. This known specified distance c is established by the blade specifications or measurements made on a master blade.

- To this end, the blade-sleeve unit is returned to position X and the measuring device 3 is returned to the 42" station. As previously described, the thrust plate A is perpendicular to the base l at this station, since, as stated,v the blade-sleeve unit is in position X with respect to the head 2. The adjacent template 3f is placed in contact with the thrust plate A, the

6 scale 3h showing the distance between said thrust plate A and the extended axis S of the sleeve I0. This distance should be a known definite distance c, as described before. Usually, however, it is not. Therefore, by tightening one of the set screws Ib and loosening the other set screw l3b, the blade 9 is pivoted about the set screws |30, Ic and i3d, i3d, the thrust plate A at the 42" station moving horizontally with respect to the extended sleeve axis S. This adjustment does not change the position of the shank surface engaged by said set screws I 3c, I3c and i3d, i3d and has substantially no eiect on the centered position of the circular section 9b with respect to the extended sleeve axis S.

This adjustment involving the use of one of the templates 3f and adjustment of the set screws lib, |317 is repeated several times, if necessary. Finally, the thrust plate A is disposed at a known, specified distance c from the extended sleeve axis at the 42;" station. Y

If the thrust plate A were of perfect contour, as is the thrust plate of a master blade, the centralization o f the circular section 9b, previously described. together with the placing of the thrust plate A at specified distance from the extended sleeve axis S at the 42" station would x the thrust plate A in desired, specified position relative to the extended sleeve axis S and said thrust plate A would be at specified distance from the extended sleeve axis S at each station along the blade surface. Usually, however, this 'is not so, due to imperfections in forming and shaping the blade.

The fifth step, therefore, is to determine the distance between the thrust plate A and the extended sleeve axis S at each station. To this end, the measuring device 3 is moved to another station. The blade-sleeve unit is then rotated with respect to the head 2,V until the surface of thethrust plate A will engage the facing edge 3g of one of the templates 3f. The distance, for example, ci of said thrust plate A from the extended sleeve axis S is then read upon the scale 3h.

In similar fashion, `readings are taken lat the other stations Ib along the base I, these readings showing the distance of the flat surface of the thrust plate A from the extended axis S of the sleeve I0 at each station.

The distances shown by these readings should agree with the blade specifications at each station within a prescribed tolerance limit, which is defined as the amount by which the distance of the thrust plate A from the extended sleeve axis S may vary from the specified distance at each station without causing rejection of theblade. Such a tolerance limit usually exists for each station, including the 42" station.

If at one or more stations, the distance, for example, ci, between the thrust plate A and the extended sleeve axis S differs from the specified distance by an amount exceeding the tolerance limitit is necessary to move said thrust plate A relative to said extended sleeve axis S until the distance therebetween is within tolerance at said last named stations.

Therefore, in the sixth step, by tightening one of the set screws |3b and loosening the other set tolerance, it is necessary to rework the blade, by l hammer or press, and then repeat the iifth and sixth steps- The reworked thrust plate A is thus brought into desired alignment with respect to the extended sleeve axis S.

The sixth step of my invention is not to be limited to adjustment ofthe set screws |3b, |31). If the circular section 9b is permitted to be slightly off-center with respect to the sleeve axis by the blade specifications, horizontal motion of the thrust plate A with respect to the extended sleeve axis may be obtained by adjustment of the set screws i3d, I 3d.

In order to properly align the leading edge B of the blade with respect to the extended sleeve axis S, the blade-sleeve unit is rotated to position Y, Fig. 2, with respect to the head 2, with the result that the thrust plate A at the 42" station becomesperpendicular to the facing edge 3g of the adjacent template 3f, in which position said facing edge 3g contacts the leading edge B of the blade. The distance between said leading edge B and the extended sleeve axis S is read upon the scale 3h. This should be a known specied distance d, but usually it is not. Therefore, by

y'tightening one of the set screws i3a and loosening the other set screw 13a. the blade is pivoted about the set screws |30, I3c and i3d, i3d, the leading edge B of the blade moving horizontally withrespect to the extended sleeve axis S. This adjustment is repeated several times, if necessary. Finally, the leading edge B is a known specified distance d from the extended sleeve axis S at the 42" station.

If the leading edge B were of perfect contour, as is the leading edge of a master blade, the setting of the leading edge B a known specified distance d from the extended sleeve axis together with the centralization of the circular section 9b would fix the leading edge B in desired specified relation to the extended sleeve axis S and the leading edge B would be separated the specified distance from the extended sleeve axis S at each station. Usually, however, this is not true due to imperfections in forming and shaping the blade.

Accordingly, the distance between the leading edge Band the extended sleeve axis S is measured at each station.

To this end, the measuring device 3 is moved upon the base l to another station. The blade, sleeve unit is rotated with respect to the reading head 2 until the surface of the thrust plate A is perpendicular to the facing edge 3g of one of the templates 3f. This is done 'b'y rotating said blade-sleeve unit, with the facing edge 3g in contact with said leading edge B until the maximum reading is obtained upon the scale 3h, this reading showing the distance dl, for example, between said leading edge B and the extended sleeve axis S.

In like manner, readings are taken at the other stations, these readings showing'the distance betweenvthe leading edge B and the extended axis S of the sleeve l0 at each station.

Those skilled in the art will recognize that these distances should equal the specified distances at each station, respectively, within prescribed tolerance limits. In a manner analogous to the vsixth step of aligningthe thrust plate A, adjustments are made to the set screws l3a, I3a and the leading edge B is moved horizontally relative to the extended sleeve axis S. It will be understood that with some blades, this horizontal motion could be obtained by adjustments to the set screws I3c, I3c. l

If, by these adjustmenta-the distance between the leading edge B and theextended sleeve axis S is brought within tolerance at all stations, d, d, etc., the leading edge B is then properly alined with respect to the extended sleeve axis S.

The blade-sleeve unit is then returned to position X, Fig. 3, and the distances c, cl, etc., between the thrust plate A and the extended vsleeve axis S are rechecked.

If these distances are not within tolerance, the blade is reworked, as by hammering, and the above'outlined adjustments relating to the thrust plate A and the leading edge B are repeated.

, If these distances are within tolerance. both the thrust plate A and the leading edge B are in correct alinement relative to the extended sleeve axisS, The blade is then ready for the lnext operation which involves use of the balance stand.

An object of my invention is to secure standard :blade characteristics by locating the center of gravity of the blade in predetermined position. Usually, for a purpose described later, it is desired to locate the center of gravity upon the extended axis of the sleeve HI. By reason of the operations previously described, the blade is usually so disposed, relative to the extended sleeve axis, that the center `of gravity either coincides with or is quite close to said extended sleeve axis. p

It is necessary, then, to ascertain whether the center of gravity of the blade coincides with the extended sleeve axis. If not, minoradjustments are made to the set screws 13a, I3a, etc., moving the blade relative to the extended sleeve axis until the center of gravity of the blade does coincide with the extended sleeve axis. I l

To this end, the blade-sleeve unit is removed from the head 2, and mounted within the balance hub 5, the shank H of the sleeve i0 being secured in seated position therein by tightening the clamp ring 5e.

The tubular balance hub 5 is so constructed that its longitudinal axis coincides with the longitudinal axis of the shaft 6 and the threaded weights 6a. Moreover, when the sleeve I0 is in described mounted position within the tubular head 5, the extended axis of the sleeve I0 coincides with the longitudinal axis of the balance hub 5.

The hub 5, shaft 6, weights 6a, sleeve l0 and blade 9 are rotatable as a unit, hereinafter referred to as the balance assembly, upon lthe ways 4b. 'Ihe extended axis of the sleeve I0 which, in view of the foregoing description, coincides Awith the axis of the balance hub 5, shaft 6 and weights 6a is dened as the longitudinal axis of the balance assembly.

As previously described the centers of gravity of the sleeve l0, hub 5, shaft 6 and weights 6a are upon their respective axes and, therefore, upon the extended axis of the sleeve Ill; Thus, without considering the blade 9, the center of gravity of the balance assembly is upon the extended axis of the sleeve l0. If the center of 9 gravity of theblade'l is 5oi'l'set `ironi'the extended axis of the sleeve I0, thecenter yci' gravity o! the balance assembly will be ofifset, Ain corresponding direction, fromv the extended axis of the sleeve i0. The balance assembly-ls rotated toa horizontal position-Fig Llandfthe` threaded weights 6d are adjusted until said balance assembly will remain at rest in ahorizontal position. In such position, the pivot of the' `balance assembly is the axis of the pin``a and the centerof gravity of the balance assembly is includedinl the vertical plane F,v Fig. '7, determined by sai'dvaxis of thepin 5a. i

The balance assembly is then placed in a vertical position,1ig.4 6,the planev P moving from a vertical to a horizontal position.

Referring now to Fig. 8,I have shown the plane P` in the last-described horizontal position. Usually, by reason of the'alinement steps previously described, the center of gravity CG of the balance assembly coincides with the extended sleeve axis S orsubstantially so. `If not, it is evident that a'torqueis exerted upon the balance assembly, this torque being expressible-as the product of the mass of the balance assembly and the'radial 'distance-R. between the center of gravity CG and the extendedsleeve axis S. This torque will 'tend to rotate the balance assembly in a vertical plane determined by said radial distance R. Alternatively, this torque could be expressed as two components, a parallel component T tendingto rotate the balance assembly in "a plane parallel'to the ways 4b and a'perpendicular component Utending to rotate' the balance 'assembly1ina plane perpendicular 'to the'ways lib.' `The balance vassembly will not rotate lin reeV spouse to the perpendicular'to'rq'ue component U due to the relation of the diametrical pin 5a to the .ways 4b, Fig. 6. However, thepar'allel torque componenthT, if `present,causes rotation o f the balance `assembly. By tightening one of the Vset screws I3b, Fig` 6, and loosening the other set screw I3b, the blade is pivoted about the set screws lic,` I3c, and i3d,` i3d, the blade moving, in the example shown, in the` direction of the arrow AW,Fig. 8, with-resultant motion of the center of gravity CG in the direction of the arrow W. This-adjustmentgis repeated several times, if necessary. Finally, a position `of thef blade relative to the extended sleeve axis S is found in which there will be no' rotation of jthe balance assembly. In -such position, the parallel torque component Tis eliminated and the center of gravity CG is laterally offset from the extended sleeve axis S, for example, at V.

The blade-sleeve unit is now rotated `through an angle of 90 degrees relativetothe hub 5 with resultant `motion of the center of gravityCG of the balance assembly from said laterally offset position V, Figs. 8 and 9, to' al transversely offset position CG, Fig. 9, relative to the extended sleeve axis S. The perpendicular torque component U, if present, is now effective in a direction parallel' to the Ways 4b and causes rotation of the balance assembly.

By tightening one of the set screws i3d, Fig. 6, and loosening the other set screw I3a, the blade is pivoted about the set screws l3c`, i3c and i3d, i3d, the blade moving, in the example shown, in the direction of the arrow Z, Fig. 9, with resultant motion of the center of gravity CG in the direction of the arrow Z. This adjustment is repeated several times, if necessary. Finally, a position of the blade relative to the extended sleeve axis S is found in which there will be no rotation of the balance assembly. In such position, the torque 10 i component U is eliminated and the center of gravity` CCfcoincidesY with the extended sleeve axis S. l

The blade sleeve unit is then removed from the balance hub 5 andv replaced in the head 2, whereupon, the respective distances of the thrust plate A, Fig.l 3, and leading edge B, Fig. 2, from the extended axis* S of the sleeve l0 are rechecked at each station. If any of these distances differ from the specified distance by an amount exceeding the allowable tolerance, the blade is reworked and the above procedure is repeated.

, If the above distances are all within tolerance,

it isclear that (1) reference surfaces have been established at specified distances. within tolerance,jfrom the extended sleeve axis S upon the thrust plate n and leading edge B of the blade 9 respectively, and (2) the `center of gravity of the blade coincides with the extended sleeve axis S.

Inforder to complete my blade balancing method, material is cut from the shank 9a of the blade, as by a lathe, and a new permanent shank surface 9c. is formed, theaxis of this permanent shank 9c coinciding with the extended axis of the sleeve I0.

Accordingly, the blade-sleeve unit is removed from the' head 2 and vplaced within the cradle B ofthe lathe, Fig. 11`. The tip oi' the blade is engaged by the clamp 8e and may be moved vertically relative to the support 8f, this motion being `coxvitrollable by the set screw 8g. Blade surfaces nearthe shank are engaged by. the set screws 8e, iicfand` 8d,`&d, adjustment of these sets of screws moving the blade vertically and horizontally, respectively. As will be understood by one skilled in machine shop' practice, the

'shank il vof `the sleeve l0 is trued up by adjustmentof the setscrewg and the set screws 8c, 8c and 8d, `8d; A common way to determine whether the sleeve shank Il is running true is to place a dial indicator i6 alternately against the two circular sections lla. The sleeve shank Ill is' running"` true, when these dial indicators show a constantreading through at least one rotation` of each of` the circular sections lla. When this is done, the extended axis of the sleeve lill` coincides with the axis of rotation of the cradle B" and the cutting tool of the lathe is adapted to form a cylindrical surface having as itsv axis the extended axis oi the sleeve I0.

` The sleeve lil is detached from the blade and the cutting tool Il, Fig. 12, is placed in contact with the shank 8d oi' the blade 9, turning out "Ua newpermanent shank 9c, the axis of which corresponds tothe former axis of the sleeve l0.

The thrust plate A and the leading edge B "arethus located in desired position relative to blade shank.

tended sleeve axis S, as shownl in Fig. 10. The angle formed by the blade center line CL and the extended sleeve axis S is usually about onehalf degree, but this has been exaggeratedxon the drawing for purpose of clarity. With such a blade, the center of gravity cg is-usually located on the center line CL. As .will be described, this involves a modification of my 'blade balancing method with respect to the use of the balance stand.

With the blade sleeve unit in seated position within the tubular hub and assuming that the center of gravity cg is located in specified position on the blade center line CL, it is evident that a torque is exerted on the balance assembly, this torque being expressible as the product of the mass of the blade and the perpendicular distance between the center of gravity CG and the extended sleeve axis S.

In accordance with my invention, the weight 5c is placed upon the pin 5b at 'such distancefrom the extended sleeve axis S that the torque exerted by this weight 5c is equal 'inmagnitude and opposite in direction relative to the torque established by the offset position of the center of gravity cg with respect to the extended sleeve axis S.

While the invention has beenl described' with respect to certain particular preferred examples .which give satisfactory results, it will be understood by those skilled in the art after understanding the invention, that variouschanges'and modifications may be made without` departing from the spirit and scope of theinvention and it is intended therefore in the appended claims to cover all such changes and modifications.

What is claimed as new and desired to be secured by Letters Patent is:

1. In the art of manufacturing metallicA propeller blades having a. cylindrical shank portion, the method of aligning the axis of rotation' of said shank portion with the center of gravity of said blade, which consists in adjustably securing the blade shank in a hollow fixture having an axis of rotation and spaced circular gaging surfaces concentric therewith, adjusting said fixture y of airfoil dimension characteristics along said'w y 369,878

blade,v comprising camber and thrust surface contour, thickness, edgealignment, width and axial center of said blade, which consists in adjustably securing the shankportion'ofa blade in a hollow fixture .havingan .axis of rotation and spaced, circular gagins surfaces rconcentric therewith, adjusting said fixture relative to said shank to bring said fixture into concentric valignment with all of said characteristics, placing said blade and attached fixturel in a metal turning machine adapted to support said blade independently of said fixture, adjustably securing said blade in said machine to bring said gaging surfaces into concentric relation with the turning axis of said machine, removing said xture from said shank and turning the surface thereof down to a nal diam-I eter concentric with and in axial alignment with allrof said characteristics.

3. In the art of `manufacturing propeller blades, the method of machining the shank surface thereof in concentria'co-axial relation with a plurality of air foil dimension characteristics along said blade comprising camber and thrust surface contour, thickness, edge alignment, width and axial center of saidblade, which consists in adjustably securing the shank portion vof a'blade in a, hollow fixture having ari-axis of rotation and concentric, spaced, circular gaging surfaces, adjusting said fixture relative to said shank to bring said gaging surfaces in concentric alignment with all of said characteristics, placing said blade and attached fixture in a metal rturning machine adapted to support said blade independently of said fixture, adjustably securing Asaid'blade in said machine at a point adjacent' eachend of said blade whereby to bring saidgaging surfaces into concentric relation with the'turnng axis of said machine, removing said `fixture from said shank and turning the .surfacethereof down to a final diameter concentric withand in axial alignment with all of said characteristics.

DAVID J. MCCOMB.

REFERENCES CITED The following: references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,836,700 Caldwell Dec. 15, 1931 1,968,540 f Squires: July 31, 1934 2,214,622 vLorenzen Sept. l0, 1940 1,968,837 Kneip Aug. 7, 1934 1,428,620 Wilber Sept. 12, 1922 1,736,247 Bodenlos Nov. 19, 1929 FOREIGN PATENTS Number Country Date l303,957 Germany Sept. 4, 1919 Great. Britain -s- Mar. 31, 1932 

